Build an Instagram Engagement Rate Calculator with Claude Code

Build an Instagram Engagement Rate Calculator web app. People search for "instagram engagement rate calculator" about 8,500 times a month, plus related searches like "instagram engagement calculator", "engagement rate formula", "instagram analytics tool". The goal is a tool that ranks for those searches and makes money.

What it should do:
Create an Instagram engagement calculator with username input or manual data entry. Include follower count, likes, comments, and post count fields. Calculate engagement rate, average likes/comments, and provide benchmarks. Show visual charts and industry comparisons. Add engagement tips and optimization suggestions. Focus on getting basic calculations working first.

How to build it:
1. Read this folder first. If it is empty, set up Next.js (App Router, TypeScript, Tailwind). Write a short PLAN.md with the pages, components, any library or API you need, and what you are leaving for later. Then build.
2. Put the tool itself on the homepage so a visitor can use it within seconds, with no sign-up. Do the processing in the browser where you can, so it is fast and cheap to run. Look at how Phlanx, Social Blade, HypeAuditor do it and make ours simpler and faster.
3. Make it rank. Use "instagram engagement rate calculator" in the title tag, H1 and meta description. Under the tool, add a short how-to and an FAQ with FAQPage schema, and add a sitemap and robots.txt. Scaffold these programmatic pages from one template and a data file: /instagram-engagement-rate-[industry], /calculate-engagement-[follower-count], /instagram-metrics-for-[niche].
4. Monetisation: Freemium: 5 calculations/day, $9/mo unlimited + reports. Add a pricing page and the free usage limit, and leave Stripe checkout as a clearly marked stub with the environment variables it needs.
5. Run it locally and test the main flow end to end, including edge cases like empty input and very large files. Fix what breaks, then finish with a summary of what works, what is stubbed and how to deploy it to Vercel.

Paste it into Claude Code in an empty folder. It plans first, so read PLAN.md and steer before it starts building.